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biochemistry > muscle fibres > Flashcards

muscle fibres Flashcards

1
Q

What is the basic structural unit of muscle tissue?

A

The muscle fiber (or muscle cell), which is a long, multinucleated cell containing many myofibrils

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2
Q

What are myofibrils?

A

Rod-like structures within muscle fibers, composed of repeating units called sarcomeres, which are responsible for muscle contraction

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3
Q

What is the sarcolemma?

A

The plasma membrane of a muscle fiber, which surrounds each muscle cell and plays a role in conducting electrical impulses.

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4
Q

What is the role of the endomysium in muscle organization?

A

A thin layer of connective tissue that surrounds individual muscle fibers, providing structural support and isolating each fiber

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5
Q

What is the perimysium?

A

A connective tissue layer that groups muscle fibers into bundles called fascicles, allowing coordinated contraction of muscle fibers within each bundle

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6
Q

What is the epimysium?

A

The outermost layer of connective tissue that surrounds the entire muscle, protecting it and helping transmit force to tendons

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7
Q

What is a sarcomere?

A

The smallest contractile unit of a muscle fiber, made up of myofilaments and extending from one Z-disc to the next

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8
Q

What are the main myofilaments in a sarcomere?

A

Thin filaments, primarily made of actin, and thick filaments, primarily made of myosin, which interact to produce contraction

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9
Q

What is the Z-disc (or Z-line)?

A

A protein structure that anchors the thin filaments and defines the boundaries of each sarcomere.

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10
Q

What is the I-band in a sarcomere?

A

The lighter region around the Z-disc where only thin (actin) filaments are present, which shortens during contraction

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11
Q

What is the A-band in a sarcomere?

A

The darker central region of the sarcomere where thick (myosin) filaments are located; its length remains constant during contraction

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12
Q

What is the H-zone in a sarcomere?

A

The central part of the A-band where there are only thick (myosin) filaments, which decreases in size during contraction.

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13
Q

What is the M-line?

A

The line in the center of the H-zone where myosin filaments are linked, helping stabilize the thick filaments within the sarcomere

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14
Q

How does the sarcomere facilitate muscle contraction?

A

Myosin heads on thick filaments bind to actin on thin filaments and pull them toward the center of the sarcomere, shortening the muscle fiber

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15
Q

What is the role of titin in sarcomere structure?

A

A large elastic protein that connects the Z-disc to the M-line, providing elasticity and helping align myosin filaments.

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16
Q

How are sarcomeres arranged within a muscle fiber?

A

Sarcomeres are aligned end-to-end along the length of each myofibril, allowing for coordinated contraction across the entire muscle fiber.

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17
Q

How do fascicles contribute to muscle structure?

A

Fascicles are bundles of muscle fibers encased by perimysium, organizing fibers within the muscle and enabling forceful contractions.

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18
Q

What is the role of actin in muscle contraction?

A

Actin forms the thin filaments in the sarcomere, providing binding sites for myosin heads during contraction, allowing cross-bridge formation and muscle shortening

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19
Q

What is the role of myosin in muscle contraction?

A

Myosin forms the thick filaments in the sarcomere; its heads bind to actin filaments, pulling them inward through power strokes, which generates the force needed for contraction.

20
Q

How are actin and myosin filaments arranged in the sarcomere?

A

Actin (thin) filaments are anchored to the Z-discs, while myosin (thick) filaments are anchored at the M-line in the center of the sarcomere. The overlapping of these filaments enables the sliding mechanism of contraction.

21
Q

What is the sliding filament theory?

A

A model describing muscle contraction where actin and myosin filaments slide past each other, shortening the sarcomere without changing the length of individual filaments.

22
Q

What is a cross-bridge in muscle contraction?

A

A connection formed when the myosin head binds to actin on the thin filament, initiating the power stroke that generates contraction.

23
Q

How does ATP facilitate muscle contraction?

A

ATP binds to myosin, allowing the myosin head to detach from actin after a power stroke. Hydrolysis of ATP then “re-cocks” the myosin head, readying it for the next cross-bridge cycle

24
Q

What is the power stroke in muscle contraction?

A

The action of the myosin head pulling actin filaments toward the M-line after binding to actin, causing sarcomere shortening and muscle contraction

25
Q

How is calcium involved in muscle contraction?

A

Calcium ions bind to troponin on the actin filament, causing a conformational change that moves tropomyosin away from myosin-binding sites on actin, enabling cross-bridge formation.

26
Q

What is the role of tropomyosin in muscle contraction?

A

Tropomyosin is a regulatory protein that blocks myosin-binding sites on actin when the muscle is relaxed, preventing contraction

27
Q

How does troponin regulate actin-myosin interactions?

A

Troponin binds calcium ions during muscle activation, causing tropomyosin to shift, which exposes myosin-binding sites on actin and allows contraction to occur.

28
Q

What happens to the sarcomere during contraction?

A

The sarcomere shortens as actin and myosin filaments slide past each other; the I-band and H-zone decrease, while the A-band remains constant

29
Q

How does sarcomere shortening lead to muscle fiber contraction?

A

As each sarcomere shortens, it pulls adjacent sarcomeres closer together, resulting in the overall shortening of the muscle fiber and generation of contractile force

30
Q

How do multiple sarcomeres contribute to whole-muscle contraction?

A

Sarcomeres are organized in series along myofibrils; simultaneous shortening of all sarcomeres in a myofibril leads to coordinated muscle fiber and whole-muscle contraction

31
Q

What is the role of the Z-disc in sarcomere organization?

A

The Z-disc anchors actin filaments and transmits force generated by the sliding of filaments to adjacent sarcomeres, maintaining structural integrity during contraction.

32
Q

What are actin-binding proteins (ABPs)?

A

Proteins that interact with actin filaments to regulate their organization, stability, and dynamics, which are essential for muscle structure and contraction

33
Q

What role does tropomyosin play as an actin-binding protein in muscle cells?

A

Tropomyosin wraps around actin filaments and blocks myosin-binding sites, preventing contraction in a relaxed muscle state

34
Q

How does troponin function as an actin-binding protein?

A

Troponin binds calcium ions and, upon activation, shifts tropomyosin away from myosin-binding sites on actin, allowing contraction to occur.

35
Q

What is the role of nebulin in actin organization?

A

stabilizes actin filaments, thereby regulating filament length

36
Q

How does titin interact with actin and myosin?

A

act as springs to keep myosin filaments centered in the sarcomere.

37
Q

What is the function of α-actinin in muscle cells?

A

α-Actinin is an actin-binding protein located at the Z-disc, where it cross-links actin filaments from adjacent sarcomeres, maintaining alignment and structural stability.

38
Q

How do capping proteins regulate actin filaments in muscle?

A

bind to the ends of actin preventing further polymerisation or depolymerisation

39
Q

What is the role of tropomodulin in muscle cells?

A

Tropomodulin caps the pointed (minus) end of actin filaments, preventing depolymerization and thus stabilizing the actin filament length within sarcomeres

40
Q

How does the actin-binding protein cofilin affect actin dynamics?

A

promotes depolymerisation and turn over

41
Q

What role does myosin light chain kinase (MLCK) play in muscle contraction?

A

MLCK phosphorylates the myosin light chains, increasing myosin’s interaction with actin and enhancing contraction, particularly in smooth muscle.

42
Q

How does calmodulin interact with actin-binding proteins?

A

Calmodulin is a calcium-binding protein that activates enzymes, including MLCK, to regulate contraction in response to calcium levels

43
Q

What is the role of dystrophin in muscle cells?

A

Dystrophin links actin filaments to the muscle cell membrane, providing structural stability and protecting the membrane from damage during contraction.

44
Q

How does the protein vinculin contribute to muscle cell integrity?

A

connects actin filaments to integrins at cell adhesion sites

45
Q

How do actin-binding proteins contribute to sarcomere stability?

A

stabilize actin filaments at the Z-disc and within sarcomeres, maintaining consistent filament length and organization

biochemistry (9 decks)

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